Impaired hand function is one of the most disabling symptoms of hemiplegic cerebral palsy (CP). It significantly affects self-care activities such as feeding, dressing, and grooming, and may limit the use of assistive technology aimed at improving quality of life. During prior work in the investigators laboratory, they observed marked improvement in performance of the more affected upper extremity during the one-hour sessions in which hand function was tested. This improvement suggests that at least part of the disability may be due to nonuse of the more affected extremity, and that this specific disability may be amenable to intervention. A recent therapeutic intervention involving restraint of the less affected extremity and extensive functional task practice with the more affected extremity, constraint-induced (CI) therapy, has been developed for adults sustaining hemiplegic stroke. This highly innovative intervention has been found to be extremely effective in overcoming nonuse of the more affected extremity in these patients. These results have compelled us to test the efficacy of this intervention in children with hemiplegic CP. However, in its existing form, it may be too intrusive for children. Thus, the overall goal of this exploratory project is to develop, improve, and test a modified form of CI therapy that is suitable for use in the children with CP. The investigators will test the hypothesis that this intervention will result in an increased amount and improved quality of function in the more affected upper extremity compared to a delayed treatment control group (specific aim 1). They will also test the hypothesis that CI therapy will be more effective in younger children with hemiplegic CP than older children due to the increased plasticity in their developing central nervous system (specific aim 2). Finally, the investigators will determine whether CI therapy is effective when modified to fit usual and customary care therapeutic schedules (specific aim 3). To determine which outcome measures are appropriate, the researchers will examine a battery of clinical tests, some of which are analogous to the tests employed in adult stroke CI studies, and others that are specifically appropriate for children with disabilities. They will also employ state-of- the-art measurement techniques to quantify reach-to-grasp and force coordination during object manipulation to determine whether the intervention results in changes in movement/force patterns. The resulting data will be used to determine inclusion and exclusion criteria, develop estimates of effect size, and refine the methods and outcome measures for future grant applications.